Imaging devices and sensor devices for the detection of radiation are often provided with elements like lenses to direct the radiation. For infrared radiation (IR) of long wavelengths in the range between 8 μm and 12 μm (LWIR), an amorphous material transmitting infrared radiation (AMTIR) like ZnSe or GeAsSe can be used to guide or focus the radiation. A mass production of such infrared detectors is prevented by prohibitive costs, which are also due to the packaging combining the detector with an integrated circuit.
A Fresnel lens comprises a plurality of concentric annular sections of different radii. Thus the continuous surface of a conventional lens is divided into annular surfaces of similar curvature, which are arranged contiguous to one another with steps in the surface where adjacent sections join. In each section the maximal thickness is considerably smaller than the maximal thickness of an equivalent conventional lens, so that the overall thickness of a Fresnel lens and hence its volume are much smaller in relation to a conventional lens.
A zone plate, sometimes called Fresnel zone plate, comprises a plurality of concentric annular sections of different radii, the so-called Fresnel zones. Opaque zones and transparent zones alternate in the area of the zone plate. Incident light is subject to diffraction around the opaque zones. The zones can be arranged so that the diffracted light constructively interferes at a desired focus.
US 2011/0147869 A1 discloses an integrated infrared-sensor comprising a Fresnel lens integrated in the rear surface of a silicon substrate. A cavity is etched into the substrate through openings in a dielectric stack. Polysilicon and titanium nitride layers extend through the openings between thermopiles arranged in the dielectric stack. A CMOS circuitry is arranged in a block of the dielectric stack.
EP 1 267 399 A2 discloses an infrared sensor comprising a resistance element in a cavity formed by a recess in a silicon substrate and by a cap body comprising a silicon substrate. The cap body carries a filter layer and a silicon layer, which is patterned to provide a Fresnel lens. A transistor is arranged on the substrate within the cavity, laterally with respect to the resistance element.
JP 2007-171174 A discloses an infrared sensing device comprising an infrared sensing part arranged in a cavity, which is formed by two silicon wafers. Through-hole wirings are electrically connected to the infrared sensing part. A semiconductor lens part is integrally formed in the upper silicon wafer.
US 2011/0147872 A1 discloses an optical device with a light receiving part arranged on a semiconductor device, which is covered with a transparent board comprising an integrated Fresnel lens. A layer of an adhesive material may comprise an opening above the light receiving part.
EP 1 079 613 A2 discloses an image input apparatus with a microlens array and a corresponding photosensitive element array.
EP 1 612 528 A2 discloses an infrared sensor comprising a sensor chip and a cap chip, which form a cavity accommodating an absorbing layer on a membrane above a recess of the sensor chip. The cap chip is provided with a lens, which can be integrated in the cap chip or in a silicon lens chip.
US 2012/0056291 A1 discloses an imaging device comprising a substrate, a photodetecting portion, a circuit portion and a through interconnect. The construction includes a lens.
US 2009/0256216 A1 discloses a wafer level chip scale package die substrate containing electronic circuits. Through-silicon vias through the substrate connect the electronic circuits to the bottom surface of the substrate. A package sensor is coupled to the substrate for sensing an environmental parameter. A protective encapsulant layer covers the top surface of the substrate except for a sensor aperture that is located above the package sensor.
U.S. Pat. No. 7,683,449 B2 discloses a radiation-detecting optoelectronic component including a semiconductor device with at least one radiation-sensitive zone configured to detect electromagnetic radiation and an optical element configured to focus the electromagnetic radiation in the radiation-sensitive zone. The optical element includes a diffractive element having structures in the same order of magnitude as the wavelength of the electromagnetic radiation.
The paper of P. M. Sarro et al.: “An integrated thermal infrared sensing array” in Sensors and Actuators 14, 191-201 (1988) reports an application of an external Fresnel zone plate for focusing infrared radiation on pixels of a detector. The spectral decomposition generated by the zone plate is used for infrared spectroscopy.
The absorption coefficient of doped silicon for infrared radiation was published by W. Spitzer and H. Y. Fan, “Infrared Absorption in n-Type Silicon,” Physical Review 108, 268-271 (1957). If the attenuation of incident radiation by free carrier absorption in silicon is desired to be smaller than 10% within a silicon thickness of 700 μm, for example, the doping concentration must be smaller than 1017 cm−3.